Biomedical subjects

S D Cook

Publications and source records attributed to S D Cook.

At least 325 records · Page 18Linked to original sources

PubMedDate not supplied

Lumbosacral fixation using expandable pedicle screws. an alternative in reoperation and osteoporosis.

BACKGROUND CONTEXT: Pedicle screw fixation in osteoporotic bone and in revision of previous pedicle screw fixation cases presents a significant challenge to spine surgeons. Biomechanical tests have shown that a pedicle screw that expands within the vertebrae body can substantially improve fixation in the presence of compromised bone. PURPOSE: To review the clinical and radiographic results with the use of expandable pedicle screws. STUDY DESIGN: One hundred forty-five patients received one or more expandable pedicle screws from the Omega21 spinal fixation system (EBI, L.P., Parsippany, NJ) to obtain thorocolumbar or lumbosacral stabilization. PATIENT SAMPLE: The indications for use of the expandable screws were osteoporosis (21 cases), reoperation of previous pedicle instrumentation (27 cases), intraoperative screw relocation (17 cases), construct reinforcement (23 cases), and sacral anchoring to avoid the necessity of anterior penetration of the sacral cortex (57 cases). OUTCOME MEASURES: The presence of radiographic fusion and complications arising from the instrumentation were reviewed at a mean follow-up period of 35 months (range, 24-72 months). METHODS: A retrospective clinical and radiographic review was performed. Fusion was evaluated based on anterior-posterior and lateral radiographs as well as dynamic radiographs in flexion and extension. RESULTS: Radiographic evidence of fusion was obtained in 125 of the 145 cases (86%). Eighty-six percent of patients with osteoporosis and 89% of reoperations fused. There were no instances of screw loosening or pullout of the expandable screws. Screw breakage occurred in four patients (2.8%), including three patients where fusion was not obtained. In six patients the expandable screws were removed without difficulty after fusion because of local discomfort. CONCLUSION: The results of this study have shown that expandable pedicle screws can be efficacious in cases in which pedicle screw fixation is difficult and adds a valuable tool to the growing armamentarium of spinal instrumentation.

Adult↗

PubMedDate not supplied

Low-intensity pulsed ultrasound improves spinal fusion.

BACKGROUND CONTEXT: Increasing the incidence of solid bony fusion is a primary goal in spine surgery. Daily low-intensity pulsed ultrasound therapy has been shown to improve and accelerate the bone healing process. PURPOSE: The purpose of this study was to evaluate the efficacy of daily low-intensity pulsed ultrasound therapy to improve the rate and quality of spinal fusion. STUDY DESIGN: Canine fusion model prospective study. PATIENT SAMPLE: Fourteen adult male dogs were used. OUTCOME MEASURES: Radiographic grading of plain films, computed tomography (CT) and magnetic resonance imaging (MRI), gross palpation, torsional stiffness and histologic grading were used to determine the presence or absence of fusion. METHODS: Posterior noninstrumented bilateral fusions were evaluated at the L2-L3 and L5-L6 levels. Treatment with low-intensity pulsed ultrasound for 20 minutes per day over the fusion site (stimulated) was compared with fusion sites that received no stimulation (nontreated controls) at 6 and 12 weeks after surgery. Plain film radiographs, CT and MRI, mechanical torsion testing and histologic examination were performed. RESULTS: At 6 weeks, ultrasound treated sites were more frequently fused compared with nontreated controls, although the difference in fusion rate was not statistically significant. At 12 weeks after surgery complete radiographic and histologic fusion occurred in 100% of ultrasound-treated sites. In the nontreated control sites 78% had achieved complete radiographic fusion and 44% had complete histologic fusion. Compared with control sites, the histological and mechanical fusion rate was significantly greater in ultrasound-treated sites (P<.05) at 12 weeks. A statistically significant increase in mechanical stiffness in ultrasound-treated sites was also found at 12 weeks after surgery. CONCLUSIONS: Low-intensity pulsed ultrasound therapy may be a useful means to ensure successful spine fusion.

Analysis of Variance↗

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Trabecular bone mineral density in idiopathic scoliosis.

The association of idiopathic scoliosis with an osteoporotic state has been indicated previously. The present study compared the trabecular bone mineral densities of 44 adolescent idiopathic scoliotic girls with 44 age-, weight-, sex-, and race-matched controls. Their lumbar spine and femoral neck bone mineral densities were evaluated using dual-photon absorptiometry. Radiographs and scoliotic curve data were also obtained for the experimental group. The scoliotic subjects exhibited significantly lower lumbar and femoral neck bone mineral densities than the control subjects. No effect was found with respect to treatment, degree, or progression of curvature. The results of this study indicate that there is a generalized state of osteoporosis in idiopathic scoliotic girls when compared with matched controls.

Adolescent↗

PubMedDate not supplied

Association of bone mineral density and pediatric fractures.

Bone mineral density in the lumbar spine and the left femoral neck was measured for a group of 17 children, 3-14 years of age, who had sustained traumatic fractures. Children with any signs of metabolic bone disease were excluded from the study. Identical measurements were made on an age- and sex-matched control population using dual photon absorptiometry. Analysis of bone mineral measurements revealed that there were no statistically significant differences between the lumbar and femoral neck densities of the two groups. The results indicate that reduced bone density is unlikely to play a significant role in acute traumatic pediatric fractures.

Adolescent↗

PubMedDate not supplied

Effects of anticonvulsant drug therapy on bone mineral density in a pediatric population.

Twenty epileptic outpatients, aged 5-20 years and taking either phenobarbital or phenytoin for anticonvulsant therapy, were evaluated for femoral neck area bone mineral content and bone mineral density using dual photon absorptiometry. Duration of treatment averaged 51.4 months (range, 9-124 months). A group of 20 normal children who were matched for age, sex, and race served as controls. There were no statistically significant differences between the femoral neck area bone mineral densities of the epileptic patients as compared to the controls. There were also no correlations between duration of anticonvulsant therapy and bone mineral density, nor any differences in bone mineral density values when comparing epileptic patients taking phenobarbital with those patients taking phenytoin.

Adolescent↗

PubMedDate not supplied

Femoral neck and lumbar spine bone mineral densities in a normal population 3-20 years of age.

Dual-photon absorptiometry (DPA) with a 153gadolinium radionuclide source was used to measure bone mineral in the lumbar spine of 109 subjects and the femoral neck of 100 subjects 3-20 years of age. From the scan data collected, multiple linear regression models were developed to predict the measured bone mineral density values as a function of age, height, and weight; male and female data were evaluated separately. From the table of predicted values, a particular subject's bone mineral measurements can be readily compared with that of normal subjects in the same way "growth charts" are commonly used to assess development.

Absorptiometry, Photon↗

PubMedDate not supplied

Lumbar spine and femoral neck bone mineral density in idiopathic scoliosis: a follow-up study.

A follow-up study of the bone mineral densities (BMD) of 22 female subjects with idiopathic scoliosis was performed using dual-photon absorptiometry at an average follow-up period of 30.8 months. Compared to the initial scans, statistically significant increases in lumbar spine and femoral neck BMD were observed. When compared to normal subjects, approximately half of the scoliotic subjects were markedly osteoporotic, having BMD measurements at least two standard deviations below the expected value. Scoliotic curvature data could not be correlated with the BMD data. The observed osteoporosis is not transient and appears characteristic of idiopathic scoliosis.

Absorptiometry, Photon↗

PubMedDate not supplied

Fatigue failure stress of the femoral neck. A case report.

Fatigue fractures are frequent injuries in military populations and occur more frequently in joggers in the civilian population. Repetitive stress below failure levels in a time period inadequate to permit remodeling is known to cause fatigue fractures. However, data on stress levels, the number of cycles to failure, and the time interval in in vivo human fatigue fractures is unknown. We recently treated a patient with a fatigue fracture of the femoral neck and were able to determine this data from patient records and finite element stress analysis. From this data we recommend a maximum total distance of 161 km (100 miles) over a three-month interval for runners who are beginning training. Shorter total distance would be advisable for obese patients.

Adult↗

PubMedDate not supplied

Shock absorption characteristics of running shoes.

The change in shock absorption properties of running shoes was evaluated as a function of miles run. Different models of running shoes encompassing a wide range in retail price were obtained and mechanically tested to simulate the repeated heel strikes of running. The energy absorbed by the shoes was determined from the area under the load deformation curve at the equivalent of 0, 5, 10, 25, 50, 75, 100, 125, 150, 200, 250, 300, and 500 miles of running. Shoes were also tested at similar intervals after having been worn by volunteers during normal training. An approximate 33% difference in the initial shock absorption was observed in the different shoe models. In general, the shoes retained approximately 75% of their initial shock absorption capability after 50 miles of simulated running, and approximately 67% after 100 to 150 miles. Between 250 and 500 miles the shoes retained less than 60% of their initial shock absorption capacity. No differences in shock absorption characteristics were apparent based upon either shoe price or the manufacturer model. The results of shoes tested by the volunteer runners also showed a marked reduction in shock absorption with mileage. The loss, however, was not as great as in the machine-simulated running, with approximately 70% of initial shock absorption retained at 500 miles.

Costs and Cost Analysis↗

PubMedDate not supplied

Biomechanical evaluation of superficial transfer of the biceps femoris tendon.

The biomechanics of the biceps femoris tendon transfer were determined from four fresh, frozen extremities. All transfers involved the proximal and anterior advancement of a selected portion of the tendon to a position superficial to the lateral collateral ligament. The rotational torque and flexion force were measured before and after the transfer with the knee positioned at 10 degrees, 20 degrees, 30 degrees, and 45 degrees of flexion, in neutral and 5 degrees internal rotation. Although more specimens need to be tested for statistical confirmation, the transfer of the superficial portion of the biceps tendon resulted in average decreases of 2% and 15% in the rotational and flexion capacity of the biceps, respectively. Biomechanically, the functional lever arm of the transferred tendon about the longitudinal (internal-external rotation) axis was essentially unchanged, while the functional lever arm about the sagittal (flexion-extension) axis was decreased slightly. The total transfer of the biceps tendon resulted in an increase of 28% in the rotational capacity, while the flexion capability was decreased an average of 75%. In addition, the total transfer resulted in the biceps becoming an extensor at 10 degrees and 20 degrees of flexion, which could actually worsen the instability. Thus, following the total transfer, the functional level arm about the sagittal axis was decreased, while the functional lever arm about the longitudinal axis was increased. In summary, neither the partial nor the total transfer of the biceps femoris tendon superficial and anterior to the fibular collateral ligament appeared to be a biomechanically effective ancillary for the treatment of anterolateral rotatory instability.

Biomechanical Phenomena↗

PubMedDate not supplied

Trabecular bone density and menstrual function in women runners.

Osteoporosis results in decreased bone mineral mass and reduced trabecular bone density. Although its etiology remains unknown, studies have revealed differential changes in the bone mineral densities of postmenopausal women, anorexic women, and amenorrheic female athletes. Correlations have also been made between estrogen deficiency and osteoporosis in both premenopausal and postmenopausal women. In order to examine the possibility of osteopenia, a group of 36 female runners between the ages of 15 and 44 years were evaluated for bone mineral density, menstrual function, and dietary habits. Serum calcium, phosphorus, and parathyroid hormone (PTH) levels were also determined for each participant, as were complete blood counts. Using dual photon absorptiometry, all participants underwent a 20 minute scan of the lumbar spine with specificity to the L1-14 vertebrae. The 36 subjects included 19 oligomenorrheic and 17 eumenorrheic women. Results of bone density analyses revealed that the oligomenorrheic runners had significantly lower calibrated bone mineral density (CBMD) than their eumenorrheic counterparts (P less than or equal to 0.01). Likewise, the PTH levels of the oligomenorrheic runners were also significantly lower (P less than or equal to 0.01). Analysis of dietary logs revealed no significant differences between the dietary habits, the calcium intake, or the caloric intake of the two groups. The data from this study indicate that there is a relationship between reduced serum PTH levels and the oligomenorrheic state. The loss of the protective effect of estrogen in the oligomenorrheic runners possibly contributed to their reduced bone mineral densities and could be a contributing factor in osteopenia.

Adolescent↗

PubMedDate not supplied

Development of lower leg strength and flexibility with the strength shoe.

The Strength Shoe is a modified athletic shoe with a 4-cm thick rubber platform attached to the front half of the sole. It is promoted as an effective method of increasing "speed, quickness, and explosive power," as well as ankle flexibility and calf circumference, when used in a plyometrics-based training regimen. This study evaluates, in a prospective, randomized trial, the efficacy and safety of the Strength Shoe training regimen for increasing lower leg flexibility and strength in intercollegiate track and field participants. No enhancement of flexibility, strength, or performance was observed for participants wearing the Strength Shoe at the end of an 8-week training program, following the suggested regimen of the manufacturer. The use of the Strength Shoe cannot be recommended as a safe, effective training method for development of lower leg strength and flexibility. However, the use of plyometrics in a properly supervised setting may improve athletic performance and merits further investigation.

Evaluation Studies as Topic↗

PubMedDate not supplied

Rheumatoid keratolysis: a series of 40 eyes.

PURPOSE: Rheumatoid keratolysis (RK) is a rare but a serious cause of ocular morbidity in rheumatoid patients. The aim of this study was to analyze the presenting features, the subsequent treatment, and the outcome of patients with RK in the authors' department. METHODS: A retrospective study was undertaken of all patients with a diagnosis of RK at Bristol Eye Hospital between January 1987 and June 2002. RESULTS: Forty eyes of 38 patients were identified in total. The mean age at presentation was 70 years. The mean duration of rheumatoid arthritis at presentation was 15 years. Most (22, 55%) ulcers were peripheral. Three patients (8%) developed RK within a month of cataract surgery. Out of the 19 patients who did not have a further RK, 11 were immunosuppressed. A total of 37 grafts were performed on 26 eyes. Twenty-two grafts (59%) failed. Immunosuppression increased the chance of anatomical success following penetrating keratoplasty. Infection was identified as a cause of graft failure for immunosuppressed patients in the postoperative period. Nine patients had reversible side effects from immunosuppressant treatment. Four eyes (10%) had to be surgically removed and a further 10 (25%) had severe visual loss (visual acuity less than 6/60). Eleven of the 38 patients subsequently died (29% mortality). CONCLUSIONS: Although the visual prognosis is often poor, surgical preservation of the eye can be achieved by penetrating keratoplasty and systemic immunosuppression. With careful observation and regular monitoring, immunosuppressive medication appears to be safely tolerated in this group of patients.

Aged↗

PubMedDate not supplied

Different therapeutic approaches and outcome in the treatment of pterygium.

PURPOSE: This study was initiated to investigate the role of different therapeutic modalities in the outcome of the surgical treatment of pterygium. METHODS: The results of treatment of pterygia with a variety of surgical techniques were studied in 56 eyes (49 patients) operated on at Bristol Eye Hospital during a period of five years. The surgical techniques included simple excision; bare sclera; conjunctival autograft; sliding conjunctival flap; lamellar keratoplasty and penetrating keratoplasty. Twelve eyes received additional beta irradiation in a fractionated total dose of 40 Gys. RESULTS: The incidence of recurrence was 23.2% for the 43 treated primary pterygia, and 23% for the 13 recurrent pterygia. All recurrences occurred between 2.5 and 11 months postoperatively. None of the 11 cases where additional beta irradiation was used showed any recurrence or other complication within the study period. In the recurrent pterygia group, the cases treated with a combination of surgical excision and beta irradiation, showed significantly lower recurrence rate (p < 0.001) compared to those cases treated with surgical excision alone. CONCLUSIONS: Beta irradiation as a complement to surgical treatment of pterygium, is successful in treating high risk cases such as reoperations, whereas for the majority of primary pterygia surgical excision alone is adequate. Additionally, follow up of one year will reveal any recurrences.

Adolescent↗

PubMedDate not supplied

Histologic and microradiographic evaluation of textured and nontextured aluminum oxide dental implants.

This paper reports the histological and microradiographical observations of macroscopically textured and nontextured aluminum oxide dental implants. Ion beam bombardment was used to produce a wafflelike pattern of surface undulations approximately 35 microns deep. Twelve nontextured and eight textured implants were placed in the healed extraction sites of the second and forth mandibular premolars of adult mongrel dogs. Eight nontextured and five textured implants remained in situ for six months. Results consistent with previously reported clinical and radiographic findings, indicated a decreased incidence of an interposed fibrous tissue-implant interface associated with the textured implants. Texturing was not found to influence the amount of vertical bone loss. Secondarily, delayed tissue fixation due to post-retrieval mechanical testing procedures resulted in loss of valuable cellular information.

Aluminum↗

PubMedDate not supplied

Fretting corrosion in orthopaedic alloys.

Fretting corrosion, a mechanical-chemical phenomenon, most often occurs at screwhead-plate countersink junctions of internal fixation devices. An apparatus was constructed which would simulate the conditions of fretting corrosion in vivo. Fretting corrosion was studied as a function of the number of cycles and the solution in which the fretting occurred. The solutions studied were 0.9% physiological saline and a saline plus 0.5% albumin solution. The implant materials tested were Co-Cr-Mo alloy, 316L stainless steel, and Ti-6A1-4V alloy. The results demonstrated that weight loss increased with the number of fretting cycles but reached a plateau where further weight loss was negligible. Co-Cr-Mo alloy showed less weight loss than 316L stainless steel at any number of cycles. Weight loss for Ti-6A1-4V alloy was similar to Co-Cr-Mo alloy although marked abrasion was noted. All of the materials showed a marked decrease in weight loss when tested in the saline plus albumin solution as compared to the saline only solution.

Alloys↗

PubMedDate not supplied

Comparison of keratometry and videokeratography after penetrating keratoplasty.

BACKGROUND: As new methods for corneal curvature measurement have evolved, users of videokeratscopes need to know the practical limitations of these instruments. We assessed agreement between keratometry and videokeratography in measuring highly astigmatic corneas. METHODS: Two independent examiners made three keratometric and videokeratographic measurements on each of 33 corneas after penetrating keratoplasty. The non-orthogonal keratometric readings obtained with a Zeiss 10 SL/O keratometer (Carl Zeiss Ltd.) were compared to the non-orthogonal simK readings (maxK, minK) calculated by the algorithms of a TMS-1 videokeratoscope (Tomey). Measurement agreement was evaluated for steep and flat meridian power and location, and astigmatism magnitude (D). RESULTS: A systematic bias of the TMS-1 in measuring steeper than keratometry for the steep meridian was demonstrated (95% confidence interval: -0.34 to -1.20 D). The limits of agreement (d - 2SD to d + 2SD) between the two instruments were found to be unacceptable for clinical purposes in measuring steep meridian power (-3.17 to +1.63 D), flat meridian power (-4.92 to +4.48 D) and astigmatism magnitude (-5.84 to +4.87 D). Clinically acceptable differences were observed in identification of steep and flat meridian location. CONCLUSIONS: The Zeiss 10 SL/O keratometer and the TMS-1 videokeratoscope showed poor measurement agreement for irregular corneal surfaces, despite the good correlation previously shown between keratometry and videokeratography in calibrated spheres and regular corneas. The TMS-1 showed a systematic bias, measuring a greater power in the steeper meridian than the Zeiss 10 SL/O keratometer. It is suggested that the two instruments cannot be used interchangeably in comparing the curvature of corneas after penetrating keratoplasty.

Adult↗

PubMedDate not supplied

Testing of an Index of Pulmonary Dysfunction in Multiple Sclerosis.

The reliability and validity of an Index of Pulmonary Dysfunction in Multiple Sclerosis (Index) comprised of four readily assessed clinical signs was studied. Forty patients with MS performed pulmonary function testing and underwent clinical evaluation to determine whether or not the Index correctly identified those patients with pulmonary dysfunction. The Index correctly predicted the presence or absence of significant respiratory muscle weakness (defined as Pemax less than 50% of predicted) in 32 (80%) of the subjects. All subjects who had normal expiratory muscle strength (Pemax greater than or equal to 80% of predicted) were correctly classified by the Index; however, not all patients with isolated expiratory muscle weakness were correctly identified. Test-retest reliability, interrater reliability (Spearman rho coefficients of 0.87 and 0.94, respectively), and internal consistency (alpha = .83) of the Index were acceptable. Index scores were not associated with changes in any other PFT results except residual volume, which increased with the severity of respiratory muscle weakness. The Index has acceptable validity and reliability for use in clinical practice to identify those neurological patients with expiratory muscle weakness.

Adult↗